I'm building a program in Unity 18.1.4f. A possibly important note is that I started building the game in Unity 17.4.2f2 and updated Unity and the brought the game up to the current version as well. Over the past week or so I've found that when I test my game, the side trigger will work the first time and I will be able to grab things. If I end the test and then run another test, the side trigger on both controllers is no longer responsive. Restarting Unity makes the side trigger responsive again for a single test. So right now I'm restarting Unity every time I want to test my changes.
I'm using the Oculus SDK.
One more note is that I have altered the OVRGrabber and OVRGrabbable scripts slightly to provide sound and haptic feedback when grabbing objects, as well as to stop an object's animation when grabbed.